The disc brake is a friction device which has been frequently used for slowing down and stopping a moving vehicle. The rotating friction surface of a disc brake is a flat, circular plate. Brake shoes are positioned on both sides of the plate and push against the plate or disc when activated. Most disc brake shoes are operated by hydraulic fluid pushing against one or more pistons, which in turn force the disc brake shoes against the sides of the disc. Thus, the braking pressure applied to the disc is brought about by pistons which force the disc brake shoes against the disc. The pistons move inside cylinders which are machined inside a casting called a caliper.
Conventionally, the piston is hollowed for much of its length in order to reduce piston weight and to provide a convenient method for piston removal. Depending on the caliper design, grooves are conventionally machined in the outside of the piston to provide a seat for either the dust boot, the piston seal, or both.
Because such pistons are subjected to repeated large forces and pressures, they must be fabricated from very hard material. Some prior art brake disc pistons have been fabricated from heavy duty steel. However, this presents problems in that the machining of the piston boot groove is an expensive and time consuming operation. Moreover, the cost of steel has risen greatly, and thus it has become abundantly desirable to produce a lightweight piston which is cheap, strong, saves metal, and yet withstands the repeated pressures and forces to which the piston will be exposed throughout the life of the disc brakes.
At least one prior art attempt primarily towards meeting the rising cost of steel has been to try to fabricate a brake disc piston from very hard plastic material. The machining of the piston boot groove in such plastic material is somewhat easier than machining in heavy duty steel, but it has been found that such plastic brake disc pistons have burned up and/or melted during actual use and tests. Moreover, the cost of plastic material is also rising because of the increased cost in petroleum from which the plastics are derived.
The present invention avoids the shortcomings and disadvantages of the prior art techniques, processes and developments, and yet achieves a lightweight, heavy duty steel brake disc piston which is cheaper and faster to manufacture.